U.S. patent number 9,655,098 [Application Number 15/072,001] was granted by the patent office on 2017-05-16 for micro base station, user terminal and radio communication method.
This patent grant is currently assigned to NTT DOCOMO, INC.. The grantee listed for this patent is NTT DOCOMO, INC.. Invention is credited to Tetsushi Abe, Satoshi Nagata, Kazuaki Takeda.
United States Patent |
9,655,098 |
Abe , et al. |
May 16, 2017 |
Micro base station, user terminal and radio communication
method
Abstract
The present invention is designed to reduce interference from a
macro base station to a small transmission power node. The present
invention is characterized in providing a micro base station which
forms, in a macro cell where a macro base station transmits a
signal to a macro terminal, a micro cell where the micro base
station transmits a signal to a micro terminal under control with
low power, and this micro base station generates a PDCCH which
includes downlink or uplink resource allocation information, and,
in a non-transmission period in which the macro base station stops
transmitting signals while leaving minimal quality measurement
signals, shifts the transmission starting symbol of the PDCCH to a
position where the PDCCH does not overlap the quality measurement
signals.
Inventors: |
Abe; Tetsushi (Tokyo,
JP), Nagata; Satoshi (Tokyo, JP), Takeda;
Kazuaki (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NTT DOCOMO, INC. |
Tokyo |
N/A |
JP |
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Assignee: |
NTT DOCOMO, INC. (Tokyo,
JP)
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Family
ID: |
46672543 |
Appl.
No.: |
15/072,001 |
Filed: |
March 16, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20160270039 A1 |
Sep 15, 2016 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13985337 |
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9326154 |
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PCT/JP2012/053293 |
Feb 13, 2012 |
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Foreign Application Priority Data
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Feb 14, 2011 [JP] |
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2011-029081 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
5/0007 (20130101); H04L 5/00 (20130101); H04W
72/1226 (20130101); H04W 16/14 (20130101); H04L
5/0053 (20130101); H04W 72/042 (20130101); H04J
11/0056 (20130101); H04L 5/0073 (20130101); H04W
48/12 (20130101); H04L 5/0035 (20130101); H04L
5/0091 (20130101); Y02D 30/70 (20200801); H04W
48/10 (20130101); H04W 24/10 (20130101); H04L
1/1812 (20130101); H04W 16/32 (20130101); H04W
88/08 (20130101) |
Current International
Class: |
H04B
7/216 (20060101); H04W 28/04 (20090101); H04L
5/00 (20060101); H04W 72/12 (20090101); H04W
16/14 (20090101); H04W 72/04 (20090101); H04W
4/00 (20090101); H04B 7/208 (20060101); H04J
11/00 (20060101); H04W 48/12 (20090101); H04W
24/10 (20090101); H04W 48/10 (20090101); H04L
1/18 (20060101); H04W 16/32 (20090101); H04W
88/08 (20090101) |
Field of
Search: |
;370/252,342,336,329
;455/434,443-444,447,450 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
International Search Report issued in PCT/JP2012/053293 mailed May
1, 2012 (2 pages). cited by applicant .
3GPP TS 36.300 V10.2.0; "3rd Generation Partnership Project;
Technical Specification Group Radio Access Network; Evolved
Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description;
Stage 2"; Dec. 2012 (200 pages). cited by applicant .
Japanese Office Action issued in Japanese Patent Application No.
2011-029081, mailing date Oct. 8, 2013, with English translation
thereof (8 pages). cited by applicant .
3GPP TSG RAN WG1 Meeting #60, R1-101106; "PDCCH Interference
Management for Heterogeneous Network;" Research in Motion UK
Limited; San Francisco, USA; Feb. 22-26, 2010 (5 pages). cited by
applicant .
3GPP TSG RAN WG1 Meeting #61, R1-102673; "Assessment of Control
Interference Coordination in Co-Channel Het-Net;" CATT; Montreal,
Canada; May 10-14, 2010 (5 pages). cited by applicant .
3GPP TSG-RAN WG1 Meeting #62, R1-104884; "Interference Coordination
for Control Channels in Macro-Femto Development;" Fujitsu; Madrid,
Spain; Aug. 23-27, 2010 (8 pages). cited by applicant .
Decision to Grant a Patent in counterpart Japanese Patent
Application No. JP2011-029081 mailed Jan. 7, 2014 (4 pages). cited
by applicant .
Office Action issued in corresponding Japanese Application No.
2013-253802, mailed Oct. 21, 2014 (8 pages). cited by applicant
.
Decision to grant a patent issued in corresponding Japanese
Application No. 2013-253802, mailed Jan. 20, 2015 (5 pages). cited
by applicant.
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Primary Examiner: Hoang; Thai
Attorney, Agent or Firm: Osha Liang LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a divisional application of and,
thereby, claims benefit under 35 U.S.C. .sctn.120 to U.S. patent
application Ser. No. 13/985,337 filed on Aug. 14, 2013, titled,
"MICRO BASE STATION, USER TERMINAL AND RADIO COMMUNICATION METHOD,"
which is a national stage application of PCT Application No.
PCT/JP2012/053293, filed on Feb. 13, 2012, which claims priority to
Japanese Patent Application No. 2011-029081, filed on Feb. 14,
2011. The contents of the priority applications are incorporated by
reference in their entirety.
Claims
The invention claimed is:
1. A radio communication control method in a user terminal, the
radio communication control method comprising the steps of:
receiving, in a specific subframe, a downlink signal having a
physical downlink data channel (PDSCH) and a physical downlink
control channel (X-PDCCH) that are frequency-division-multiplexed
and allocated to a first radio resource, from a first symbol in the
first radio resource, the first radio resource being a data region
corresponding to symbols following a first predetermined number of
symbols in the specific subframe, and receiving, in another
specific subframe, a downlink signal having a physical downlink
data channel (PDSCH) and a physical downlink control channel
(X-PDCCH) that are frequency-division-multiplexed and allocated to
a second radio resource, the second radio resource being an
enhanced data region corresponding to first to last symbols in the
other specific subframe in which allocation of the physical
downlink data channel (PDSCH) starts with any symbol among a first
predetermined number of symbols in the second radio resource, and
allocation of the physical downlink control channel (X-PDCCH)
starts with a symbol following the first predetermined number of
symbols in the second radio resource; and specifying the physical
downlink control channel (X-PDCCH) from the received downlink
signal based on information about a physical downlink control
channel (X-PDCCH) configuration given from a radio base station by
higher layer signaling, wherein the user terminal is switchable
between a configuration where allocation of the PDSCH starts with a
same symbol as allocation of the X-PDCCH in the specific subframe
and a configuration where allocation of the PDSCH starts with an
earlier symbol than allocation of the X-PDCCH in the other specific
subframe.
2. A user terminal comprising: a receiving section that receives,
in a specific subframe, a downlink signal having a physical
downlink data channel (PDSCH) and a physical downlink control
channel (X-PDCCH) that are frequency-division-multiplexed and
allocated to a first radio resource, from a first symbol in the
first radio resource, the first radio resource being a data region
corresponding to symbols following a first predetermined number of
symbols in the specific subframe, and receives, in another specific
subframe, a downlink signal having a physical downlink data channel
(PDSCH) and a physical downlink control channel (X-PDCCH) that are
frequency-division-multiplexed and allocated to a second radio
resource, the second radio resource being an enhanced data region
corresponding to first to last symbols in the other specific
subframe in which allocation of the physical downlink data channel
(PDSCH) starts with any symbol among a first predetermined number
of symbols in the second radio resource, and allocation of the
physical downlink control channel (X-PDCCH) starts with a symbol
following the first predetermined number of symbols in the second
radio resource; and a processing section that specifies the
physical downlink control channel (X-PDCCH) from the received
downlink signal based on information about a physical downlink
control channel (X-PDCCH) configuration given from a radio base
station by higher layer signaling, wherein the user terminal is
switchable between a configuration where allocation of the PDSCH
starts with a same symbol as allocation of the X-PDCCH in the
specific subframe and a configuration where allocation of the PDSCH
starts with an earlier symbol than allocation of the X-PDCCH in the
other specific subframe.
Description
TECHNICAL FIELD
Embodiments of the present invention relate to a micro base
station, a user terminal and a radio communication method in a
radio communication system in which a micro cell is overlaid in a
macro cell.
BACKGROUND ART
Presently, in the 3GPP (Third Generation Partnership Project), the
standardization of LTE-advanced (hereinafter the LTE Release 10
specifications and the specifications of later versions will be
collectively referred to as "LTE-A"), which is an evolved radio
interface of the LTE (Long Term Evolution) Release 8 specifications
(hereinafter referred to as "LTE" or "Rel. 8") is in progress.
LTE-A is attempting to realize higher system performance than LTE
while maintaining backward compatibility with LTE.
Also, in LTE-A, a micro cell (for example, a pico cell, a femto
cell, and so on), which has a local coverage area of a radius of
approximately several tens of meters, is formed in a macro cell,
which has a wide coverage area of a radius of approximately several
kilometers. A network configuration such as this in which nodes of
different powers are overlaid is referred to as a "HetNet"
(Heterogeneous Network) (see, for example, non-patent literature
1). A normal radio base station to form a macro cell will be
hereinafter referred to as a "macro base station," and a pico base
station or a femto base station of lower transmission power will be
hereinafter referred to as a "small transmission power node." Small
transmission power nodes include a base station antenna apparatus
(RRH: Remote Radio Head). A base station antenna apparatus is a
small transmission power node that is set in a distant location
from a macro base station using optical fiber and so on, and forms
a micro cell under control of a macro base station.
CITATION LIST
Non-Patent Literature
[Non-Patent Literature 1] 3GPP, TS36.300
SUMMARY OF INVENTION
However, in a HetNet, in which a micro cell that is formed by a
small transmission power node having low transmission power is
overlaid in a macro cell that is formed by a macro base station
having high transmission power, there is a problem that severe
interference is given from the macro base station having higher
transmission power, to the small transmission power node.
The present invention has been made in view of the above, and it is
therefore an object of the present invention to provide a micro
base station, a user terminal and a radio communication method,
which can reduce interference from a macro base station to a small
transmission power node.
A micro base station according to the present invention is a micro
base station which forms, in a macro cell where a radio base
station transmits a signal to a terminal with first transmission
power, a micro cell where the micro base station transmits a signal
to a terminal under control with second transmission power, which
is lower than the first transmission power, and this micro base
station has: a downlink control information generating section,
which generates a downlink control channel signal including
downlink or uplink resource allocation information, a control
section, which, in a specific subframe, shifts a transmission
starting symbol of the downlink control channel signal to a
position where the downlink control channel signal does not overlap
a quality measurement signal that is transmitted in the macro cell,
and a radio transmitting section, which transmits the downlink
control signal, in which the transmission starting symbol has been
shifted, by radio transmission.
By means of this configuration, it is possible to prevent a
collision between a quality measurement signal that is arranged in
the top symbol of a specific subframe of a macro cell, and a
downlink control channel that is arranged in the top several
symbols of a micro cell subframe that is synchronized with the
specific subframe from, and prevent deterioration of downlink
control channel demodulation.
According to the present invention, it is possible to reduce
interference from a macro base station to a small transmission
power node.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1A and 1B are diagrams to show interference coordination in a
HetNet;
FIGS. 2A and 1B are diagrams to show a schematic configuration of a
HetNet;
FIG. 3 is conceptual diagram in which the PDCCH starting position
is shifted;
FIG. 4A is conceptual diagram in which part of resource elements is
subject to rate matching in a system defining a downlink control
channel in a data field, and FIG. 4B is a conceptual diagram in
which the first OFDM symbol is subject to rate matching;
FIG. 5A is a conceptual diagram in which rate matching is not
performed in a system in which a macro cell and a micro cell use
the same cell ID, and FIG. 5B is a conceptual diagram in which a
PDCCH arrangement field is subject to rate matching in a system
where a macro cell and a micro cell use the same cell ID;
FIG. 6 is a diagram to show a schematic configuration of a
HetNet;
FIG. 7 is a functional block diagram of a macro base station and a
micro base station (RRH);
FIG. 8 is a detailed functional block diagram of a base
station;
FIG. 9 is a functional block diagram of an OFDM modulation section
in a base station;
FIG. 10 is a functional block diagram of a user terminal;
FIG. 11 is a detailed functional block diagram of a user terminal;
and
FIG. 12 is a functional block diagram of a macro base station and a
pico base station.
DESCRIPTION OF EMBODIMENTS
An HetNet is a layered network, which overlays cells of various
forms such as a micro cell C2 (small-sized cell: a pico cell, a
femto cell, an RRH cell, and so on), on top of an existing macro
cell C1 (large-sized cell), as shown in FIG. 6. In this HetNet, the
downlink transmission power of the macro base station B1 of the
macro cell C1, which covers a relatively wide area, is set greater
than the micro base station B2 of the micro cell C2, which covers a
relatively narrow area.
In this way, the HetNet is a layered network, in which the micro
base station B2 having lower transmission power (and cell area) is
present under the macro base station B1 having greater transmission
power (and cell area). In the layered network, there is a problem
that a UE that is in a cell edge of the micro cell C2 is unable to
connect with the micro cell C2, although the UE is located in a
close position to the micro base station B2. In the cell edge of
the micro cell C2, the transmission power of the macro base station
B1 is greater than the transmission power of the micro base station
B2. As a result of this, the UE at the cell edge of the micro cell
C2 is unable to catch the radio frames from the micro base station
B2 of the pico cell C1, and connects with the macro cell C1 by
catching the radio frames from the macro base station B1 of greater
transmission power. This means that the original area of the micro
cell C2 is invaded by the macro base station B1 and is becoming
smaller.
FIGS. 1A and 1B are conceptual diagrams of interference
coordination for reducing interference from the macro base station
B1 of greater transmission power, against the micro base station
B2. In LTE, a MBSFN (Multimedia Broadcast multicast service Single
Frequency Network) subframe is standardized. An MBSFN subframe is a
subframe which can be made a blank period except for the control
channel. A subframe (ABS: Almost Blank Subframe) to serve as a
non-transmission period is provided in a radio frame to be
transmitted by the macro base station B1, using an MBSFN subframe,
and the radio resource of the ABS period is allocated to a micro UE
that is located near the cell edge of the micro cell C2. It is
possible to transmit reference signals (cell-specific reference
signals (CRSs), positioning reference signals, and so on), the
synchronization signal, the broadcast channel and paging, in an ABS
period, but no others (the data channel and so on) are
transmitted.
When the radio resource of the ABS period is assigned to the UE
located near the cell edge of the micro cell C2, in the ABS period,
the UE is able to connect with the micro cell C2 without being
influenced by the transmission power of the macro base station B1.
On the other hand, even when radio resources outside the ABS period
are assigned to a UE located near the cell center of the micro cell
C2, the transmission power from the micro base station B2 is
greater than the transmission power from the macro base station B1,
and therefore the UE is able to connect with the micro cell C2.
FIG. 1A shows the configurations of a downlink physical control
channel and a downlink physical shared data channel in the macro
base station B1. FIG. 1B shows the configurations of a downlink
physical control channel and a downlink physical shared data
channel in the micro base station B2. The transmission time units
(subframes) of the macro base station B1 and the micro base station
B2 are synchronized, the macro base station B1 applies an ABS, in
which signals other than CRSs stop being transmitted, in specific
subframe #4, to reduce interference against the micro cell C2, and,
MBSFN subframes, in which the CRSs of the data field are removed,
to specific subframes #1, #2, #6, #7 and #8, so that it is possible
to further reduce the interference against the micro cell C2.
Now, near the cell edge of the micro cell C2, the influence of the
transmission power from the macro base station B1 is significant,
and yet, near the cell center of the micro cell C2, interference
from the macro base station B1 is insignificant. Consequently, near
the cell edge of the micro cell C2, although the received SINR
increases in an ABS period, the received SINR nevertheless
decreases outside the ABS period. In the following descriptions, in
a micro cell subframe (TTI in a small cell such as a pico cell, a
femto cell, an RRH cell and so on), a period in which signals
transmitted from a small transmission power node are protected from
macro interference will be referred to as a "protected subframe,"
and a subframe, in which no special measure is taken to protect
signals transmitted from a small transmission power node from macro
interference, will be referred to as a "non-protected subframe" or
a "normal subframe."
FIG. 2A shows a state of a non-protected subframe sent from a macro
base station to a user terminal (macro UE) under the macro base
station by radio transmission. Non-protected subframes are, for
example, macro cell subframe #0 and micro cell subframe #8 shown in
FIGS. 1A and 1B. The macro base station B1 performs radio
transmission by high transmission power, in non-protected
subframes, to the macro UE. Consequently, the micro base station B2
and the micro UE suffer severe interference.
FIG. 2B shows a state of protected subframes, in which the macro
base station B1 stops radio transmission to the user terminal
(macro UE) under the macro base station. Protected subframes are,
for example, macro cell subframe #1 and micro cell subframe #9
shown in FIGS. 1A and 1B. In protected subframes, the macro base
station B1 stops transmitting the PDSCH (ABS), and, except in the
top OFDM symbol, stops transmitting the CRSs (MBSFN). Consequently,
interference against the micro base station B2 and the micro UE is
reduced. The micro base station B2 performs radio transmission to
the micro UE under the micro base station in protected subframes,
so that radio communication to prevent interference from the macro
base station B1 is expected to be made possible.
Now, even if the macro base station applies ABS/MBSFN subframes to
specific subframes, interference from the macro base station to a
small transmission power node, which is a micro base station, still
remains. For example, as shown in FIG. 1A, CRSs, arranged in the
top OFDM symbol of an ABS/MBSFN subframe, interfere with the top
first to third OFDM symbols of a corresponding subframe of a micro
cell, and damage the demodulation of the physical downlink control
channel (PDCCH: Physical Downlink Control Channel) arranged in the
top first to third OFDM symbols of a subframe in the micro cell.
Also, when the macro base station transmits the PDCCH of uplink
allocation (UL grant) in, for example, macro cell subframe #0, the
macro UE to receive this PDCCH transmits uplink data four subframes
later. The macro base station furthermore transmits an Ack/Nack in
response to the uplink data to the macro UE in the PHICH (Physical
Hybrid ARQ Indicator Channel) arranged in the top OFDM symbol in
macro cell subframe #8 four subframes later. As shown in FIG. 1A,
there is a possibility that an ABS subframe (subframe #8) and the
PHICH collide. When an ABS subframe and the PHICH collide, the
PHICH interferes with the pico cell.
The first aspect of the present invention is that, although, in a
specific subframe of the macro cell, at least a downlink reference
signal is arranged in the top symbol, in a synchronized specific
subframe of the micro cell, the symbol starting position of the
physical downlink control channel (for example, the PDCCH supported
in LTE) is arranged to be shifted from the top symbol. The specific
subframes are either protected subframes or non-protected
subframes.
By this means, it is possible to prevent a collision of the CRSs
(or the CRSs and the PHICH) arranged in the top OFDM symbol of a
specific subframe (for example, ABS/MBSFN subframe) of the macro
cell and the physical downlink control channel to be arranged in
the top first to third OFDM symbol of a specific subframe of the
micro cell, and prevent deterioration of the demodulation of the
physical downlink control channel.
FIG. 3 is a conceptual diagram in which the PDCCH starting position
in a micro cell subframe is shifted. Note that, although RRH/pico
base stations are exemplified as small transmission power nodes to
form micro cells, other small transmission power nodes are equally
applicable. The macro cell subframe configuration will be described
first. As shown in the upper part of FIG. 3, in a non-protected
subframe, the PDCCH is arranged in the top first to third OFDM
symbols (control field) and the PDSCH is arranged in the rest of
the data field. CRSs are arranged over the entire subframe (the
time domain and the frequency domain). The subcarrier positions of
the CRSs shift depending on cell IDs. The synchronization signals
(PSS and SSS) are multiplexed on the central six RBs (1.08 MHz). On
the other hand, in a protected subframe, in an ABS+MBSFN subframe,
CRSs are arranged in the top OFDM symbol alone and are not arranged
in the data field. In the example shown in FIG. 3, the PHICH is
multiplexed on the top OFDM symbol of the second subframe. The
PHICH is used to transmit hybrid ARQ acknowledgment response, which
is a response to UL-SCH (Uplink Shared Channel) transmission. To
allow the hybrid ARQ protocol to operate adequately, it is
necessary to keep the PHICH error rate sufficiently low. Normally,
the PHICH is transmitted only in the top OFDM symbol of a subframe,
so that a user terminal is able to try decoding the PHICH even when
the user terminal fails to decode the PCFICH. Note that the PHICH
is arranged in subframe #n+8, which is eight subframes after
subframe #n in which a UL grant is transmitted.
Next, the micro cell subframe configuration will be described. As
shown in the lower part of FIG. 3, in a non-protected subframe, the
starting symbol of the PDCCH is changed from the top of a subframe
to the second OFDM symbol. The PDCCH is arranged in the second OFDM
symbol (up to the third OFDM symbol, at a maximum), which is one
symbol shifted from the top OFDM symbol, and the PDSCH is arranged
in the rest of the data field. Consequently, the PDCCH arranged in
the micro cell subframe is protected from interference from the
CRSs and the PHICH arranged in the top OFDM symbol of the macro
cell-subframe. The CRSs are arranged in the top OFDM symbol. The
CRSs arranged in the micro cell subframe are arranged in different
subcarrier positions from the CRSs arranged in the micro cell
subframe, because the macro cell and the micro cell have different
cell IDs. Consequently, the micro UE is able to accurately decode
the CRSs arranged in the micro cell subframe.
Note that, in the micro cell, the subframes where change of the
PDCCH to shift the starting symbol of the PDCCH from the top OFDM
symbol, does not have to be all protected subframes. In the example
shown in FIG. 3, the PDCCH change is applied only to the subframe
arranged in the middle of three subframes. The subframe to which
the PDCCH change is applied may be all non-protected subframes as
well.
The micro base station notifies the starting position of the PDCCH
in the specific subframe where the PDCCH change is applied, to the
micro UE under the micro cell. Various methods are applicable as
methods of reporting the PDCCH starting position. For example, the
subframe numbers to apply the PDCCH change to and the PDCCH
starting position may be determined, in advance, in specifications,
on a fixed basis, and a user terminal to support the specifications
changes the PDCCH starting position according to the subframe
numbers (for example, even numbers) and performs decoding. Also,
the subframe numbers to apply the PDCCH change to and the PDCCH
starting position may be reported from the micro base station to
the micro UE via higher layer signaling. Use of higher layer
signaling allows semi-statistic switching.
Upon receiving the specific subframe where the PDCCH change is
applied, the micro UE uses the second OFDM symbol from the top as
the starting symbol of the PDCCH, and performs decoding. By this
means, even when the CRSs and PHICH are arranged in the top OFDM
symbol of a macro cell subframe, the PDCCH of a micro cell subframe
can be decoded accurately.
A second aspect of the present invention is that, in a macro cell
subframe that is synchronized with a specific subframe (a protected
subframe or a non-protected subframe), at least a downlink
reference signal is arranged in the top symbol in a macro cell
subframe, in a micro cell subframe that is synchronized with the
specific subframe, a physical downlink control channel is arranged
in a data field that does not overlap the control field (the top
first to third symbols), and the data channel is expanded to the
control field.
By this means, it is possible to prevent a collision of the CRSs
(or CRSs and PHICH) that are arranged in the top OFDM symbol of a
specific subframe (for example, an ABS/MBSFN subframe) of the macro
cell, and the physical downlink control channel that is arranged in
the data field (the field from the third OFDM symbol from the top
and onward) of a micro cell subframe that is synchronized with the
specific subframe, and prevent the demodulation of the physical
downlink control channel in the micro cell from deteriorating.
Also, since the data channel is allocated to empty resources in the
control field where the PDCCH is arranged, efficient use of
resources is made possible.
FIGS. 4A and 4B are conceptual diagrams in which, in a micro cell
subframe, the downlink control channel is defined in the data
field, and part of the data channel is arranged in the control
field where the PDCCH is defined. Note that, although an RRH is
exemplified as a small transmission power node to form a micro
cell, other small transmission power nodes are equally
applicable.
FIG. 4A shows an example of arranging a data channel (PDSCH) from
the top OFDM symbol of a micro cell subframe, and FIG. 4B shows an
example of arranging a data channel (PDSCH) from the second OFDM
symbol of the micro cell subframe. The macro cell subframe
configuration shown in the upper part of FIG. 4A is basically not
different from the macro cell subframe configuration shown in the
upper part of FIG. 3 described above.
In the micro cell subframe configuration shown in the lower part of
FIG. 4A, a new physical channel is defined with respect to a micro
cell subframe that is synchronized with the protected subframe. The
newly defined physical channel will be described in detail. In the
data field (the symbol field of the second or the third OFDM symbol
and onward) of an existing subframe, a new physical downlink
control channel (hereinafter referred to as "X-PDCCH") is defined.
The X-PDCCH is allocated the resources from the end of the control
field of the legacy subframe to the final symbol of that subframe,
in the time domain. Also, the X-PDCCH is allocated to a plurality
of subcarriers near the center of the system band, in the frequency
domain. A reference signal (DM-RS: Demodulation Reference Signal)
for downlink demodulation, which is one of the downlink reference
signals, is arranged over the entire system band. The PDCCH is a
user-specific control channel, so that the DM-RS, which is a
user-specific downlink reference signal, has high affinity as a
reference signal for demodulation of the X-PDCCH. However, if the
X-PDCCH can be demodulated, the other downlink reference signals
(CRSs and so on) can be used as well.
The data channel (PDSCH) is allocated to the control field (the
field from the first OFDM symbol to the third OFDM symbol at a
maximum) of an legacy subframe. It is also possible to say that the
data field is expended to the first OFDM symbol of a subframe. When
the macro cell and the micro cell have varying cell IDs, the
subcarrier positions to arrange the CRSs also shift, so that, when
a data channel is arranged in empty resource elements, interference
with the CRSs transmitted in the macro cell subframe is created.
Consequently, the resource elements to collide with the CRSs
transmitted in the macro cell subframe (the first OFDM symbol) are
muted. The capacity in which the data channel can be allocated
decreases for the number of resource elements to be muted. So, the
RRH (micro base station) performs rate matching of the resource
elements to be muted, and encodes the data channel into an amount
of data to match the capacity secured for data channel
transmission.
The RRH (micro base station) reports the specific subframe to which
the X-PDCCH is applied, and muting resource elements, to the micro
UE under the micro cell. Identification information of the rate
matching scheme can be transmitted by the X-PDCCH. Various methods
are applicable as methods of reporting the specific subframe to
which the X-PDCCH is applied. For example, the subframe number to
apply the X-PDCCH to may be determined in advance, by
specifications, on a fixed basis, and a user terminal to support
the specifications may decode the X-PDCCH in accordance with the
subframe numbers (for example, even numbers), switch the rate
matching method of the data channel and decode (performs de-rate
matching of) the data channel. Also, the subframe numbers to apply
the X-PDCCH to may be reported from the RRH (micro base station) to
the micro cell UE via higher layer signaling. Use of higher layer
signaling allows semi-statistic switching.
Upon receiving the specific subframe where the X-PDCCH is applied,
the micro cell UE receives the X-PDCCH from the top symbol (the
third or fourth OFDM symbol) of the data field and performs
decoding. The rate matching method (identification information)
included in the X-PDCCH is acquired, and, by applying de-rate
matching corresponding to the rate matching method, the data
channel is demodulated.
FIG. 4B shows an example of arranging the data channel (PDSCH) from
the second OFDM symbol of the micro cell subframe. The macro cell
subframe configuration shown in the upper part of FIG. 4B is the
same as the macro cell subframe configuration shown in the upper
part of FIG. 3.
In the micro cell subframe configuration shown in the lower part of
FIG. 4B, the X-PDCCH, which is a physical channel, is newly defined
with respect to a micro cell subframe that is synchronized with a
protected subframe. As has been described with reference to FIG.
4A, the X-PDCCH is allocated the resources from the end of the
control field of an legacy subframe to the final symbol of that
subframe, in the time domain. Also, the X-PDCCH is allocated to a
plurality of subcarriers near the center of the system band, in the
frequency domain.
On the other hand, the data channel (PDSCH) is allocated up to the
second OFDM symbol, which serves as the control field, in an legacy
subframe. It is also possible to say that the data field is
expanded to the second OFDM symbol of a subframe. As shown in FIG.
4B, in a specific subframe in a macro cell, there is a possibility
that the PHICH is arranged in the first OFDM symbol. In that
specific subframe, CRSs and PHICH are multiplexed on the first OFDM
symbol, so that there is severe interference against the first OFDM
symbol of the micro cell subframe. So, in a specific subframe (in
the present example, a protected subframe) where CRSs and PHICH are
arranged in the first OFDM symbol of a macro cell subframe, it is
preferable to expand the data channel (PDSCH) to the second OFDM
symbol.
The capacity in which the data channel can be allocated decreases
for the number of resource elements of the first OFDM symbol. So,
the RRH (macro base station) subjects all of the first OFDM symbol
to rate matching and encodes the data channel into an amount to
match the capacity secured for data channel transmission.
The RRH (micro base station) reports the specific subframe to which
the X-PDCCH is applied, to the micro UE under the micro cell.
Identification information of the rate matching scheme can be
transmitted by the X-PDCCH. Various methods are applicable as
methods of reporting the specific subframe to apply the X-PDCCH
to.
Upon receiving the specific subframe where the X-PDCCH is applied,
the micro UE receives and decodes the X-PDCCH from the top symbol
(the second OFDM symbol) of the data filed. The rate matching
method included in the X-PDCCH (identification information) is
acquired, and, by applying de-rate matching to correspond to the
rate matching method, the data channel is demodulated.
The rate matching to support the interference coordination shown in
FIG. 4A will be referred to as "the first rate matching method,"
and the rate matching to support the interference coordination
shown in FIG. 4B will be hereinafter referred to as "the second
rate matching method." The macro base station handles the baseband
processing of the physical channel signal to be transmitted from
the RRH in the macro base station, so that it is possible to select
between the interference coordination shown in FIG. 4A and the
interference coordination shown in FIG. 4B on a dynamic basis. In
this case, in accordance with the selection of interference
coordination, the rate matching method needs to be switched as
well, but if the macro base station handles this, it is possible to
switch between the first rate matching method and the second rate
matching method quickly, on a dynamic basis. Note that a pico base
station, which is a small transmission power node, is connected
with the macro base station via an X2 interface, and therefore is
able to switch rate matching.
FIGS. 5A and 5B are conceptual diagrams of defining a downlink
control channel in a data field and arranging part of a data
channel in a control field, showing an example where the macro cell
and the micro cell use the same cell ID. When a macro cell and a
micro cell use the same cell ID, the micro cell transmits the same
CRSs and PDCCH as the macro cell. However, the present invention is
not limited to the case of using the same cell ID, and is
applicable to cases of using different cell IDs.
In FIG. 5A, in a specific subframe (a protected subframe in the
present example), in the macro cell, CRSs are transmitted in the
first OFDM symbol, and, in the micro cell, too, CRSs are arranged
in the same resource as in the macro cell. The RRH arranges the
X-PDCCH in the data field of a micro cell subframe, and executes
scheduling such that the data channel (PDSCH) is expanded to the
first OFDM symbol. In this case, given that the resource elements
where CRSs are arranged are the same as in the macro cell, the
resource elements to be muted in the control field of the micro
cell subframe are CRSs alone. At this time, rate matching is
applied only to the CRSs of the control field.
In FIG. 5B, although, in a specific subframe (a protected subframe
in the present example), although, in the macro cell, CRSs are
transmitted in the first OFDM symbol and furthermore the PDCCH is
also transmitted, in the micro cell, CRSs and PDCCH are also
arranged in the same resource as in the macro cell. The macro base
station, for example, does not transmit the PDCCH in a protected
subframe, but the macro base station does not prohibit this
completely, and, instead, as shown in the macro cell subframe of
FIG. 5B, the macro base station is preferably able to transmit the
PDCCH in protected subframes when necessary. The RRH arranges the
X-PDCCH in the data field of the micro cell subframe, arranges CRSs
and PDCCH in the original control field up to the third OFDM symbol
at a maximum, and schedules the data channel (PDSCH) from the top
of the data field, which starts from the end of the PDCCH. In this
case, the capacity decreases below the basic capacity of the data
channel for the resource elements where the PDCCH is arranged.
Consequently, as shown in FIG. 5B, when the data channel is started
from the end of the PDCCH, the whole of the PDCCH arrangement field
is subject to rate matching. That is to say, the RRH (micro base
station) performs rate matching for all of the arrangement field of
the PDCCH, and encodes the data channel to match the capacity
secured for data channel transmission.
The rate matching to support the interference coordination shown in
FIG. 5A will be referred to as "the third rate matching method,"
and the rate matching to support the interference coordination
shown in FIG. 5B will be hereinafter referred to as "the fourth
rate matching method." The macro base station handles the baseband
processing of the physical channel signal to be transmitted from
the RRH in the macro base station, so that the macro base station
is able to select between the interference coordination shown in
FIG. 5A and the interference coordination shown in FIG. 5B on a
dynamic basis, and switch between the third rate matching method
and the fourth rate matching method quickly. Note that a pico base
station, which is a small transmission power node, is connected
with the macro base station via an X2 interface, and therefore is
able to switch rate matching.
Also, the above X-PDCCH is not only applicable to a micro cell
subframe that is synchronized with a protected subframe, but is
also applicable to a micro cell subframe that is synchronized with
a non-protected subframe.
The present invention is applicable to the LTE/LTE-A system, which
is one next generation mobile communication system. First, an
overview of the LTE/LTE-A system will be described. Note that, in
the following descriptions, a fundamental frequency block will be
described as a component carrier.
In the present system, an LTE-A system, which is the first
communication system having the first system band that is formed
with a plurality of component carriers and that is relatively wide,
and an LTE system, which is a second communication system having a
second system band that is relatively narrow (and that is formed
with one component carrier here), coexist. In the LTE-A system,
radio communication is carried out using a variable system
bandwidth of maximum 100 MHz, and, in the LTE system, radio
communication is carried out in a variable system bandwidth of
maximum 20 MHz. The system band of the LTE-A system is at least one
fundamental frequency block (component carrier: CC), where the
system band of the LTE system is one unit. Coupling a plurality of
fundamental frequency blocks into a wide band as one in this way is
referred to as "carrier aggregation."
For radio access schemes, OFDMA (Orthogonal Frequency Division
Multiple Access) is adopted on the downlink, and SC-FDMA
(Single-Carrier Frequency Division Multiple Access) is adopted on
the uplink, but the uplink radio access scheme is by no means
limited to this. OFDMA is a multi-carrier transmission scheme to
perform communication by dividing a frequency band into a plurality
of narrow frequency bands (subcarriers) and placing data on each
frequency band. SC-FDMA is a single carrier transmission scheme to
reduce interference between terminals by dividing, per terminal,
the system band into bands formed with one or continuous resource
blocks, and allowing a plurality of terminals to use mutually
different bands.
Here, channel configurations in the LTE system will be described.
Downlink channel configurations will be described first. The
downlink channels include a PDSCH (Physical Downlink Shared
Channel), which is used by user terminals in a cell on a shared
basis, as a downlink data channel, and downlink L1/L2 control
channels (PDCCH, PCFICH, and PHICH). Transmission data and higher
control information are transmitted by the PDSCH. The scheduling
information of the PDSCH, the PUSCH and so on are transmitted by
the PDCCH (Physical Downlink Control Channel). The number of OFDM
symbols to use for the PDCCH is transmitted by the PCFICH (Physical
Control Format Indicator Channel). HARQ ACK/NACK for the PUSCH are
transmitted by the PHICH (Physical Hybrid-ARQ Indicator
Channel).
Uplink channel configurations will be described. The uplink
channels include a PUSCH (Physical Uplink Shared Channel), which is
used by user terminals in a cell on a shared basis as an uplink
data channel, and a PUCCH (Physical Uplink Control Channel), which
is an uplink control channel. By means of this PUSCH, transmission
data and higher control information are transmitted. Also, by the
PUCCH, the CSI, which is received quality information measured from
downlink reference signals (CSI-RS and CRS), downlink radio quality
information (CQI: Channel Quality Indicator), ACK/NACK, and so on
are transmitted.
Now, a radio communication system according to an embodiment of the
present invention will be described in detail. Note that the radio
communication system shown in FIG. 6 is a system to accommodate,
for example, the LTE system or SUPER 3G. This radio communication
system uses carrier aggregation, which makes a plurality of
fundamental frequency blocks, in which the system band of the LTE
system is one unit, as one. Also, this radio communication system
may be referred to as "IMT-Advanced" or "4G."
The macro base station B1 is connected with an upper station
apparatus, and this upper station apparatus is connected with a
core network. The channels are controlled such that a macro UE
under the macro base station B1 is able to communicate with the
macro base station B1, and a micro UE under the micro base station
B2 is able to communicate with the micro base station B2. Note that
the upper station apparatus includes, for example, an access
gateway apparatus, a radio network controller (RNC), a mobility
management entity (MME) and so on, but is by no means limited to
these. The user terminal (macro UE/micro UE) supports LTE/LTE-A,
unless specified otherwise.
With reference to FIG. 7, overall configurations of the macro base
station and the micro base station (RRH) according to the present
embodiment will be described. The macro base station B1 includes a
macro base station section 20 for communicating with user terminals
under the macro cell, and part of the functional elements
(functional sections, not including the functions of the radio
part) of RRHs 30 and 31 (micro base stations B2 and B3 shown in
FIG. 6, and so on) connected with the macro base station B1 by
cables L1 and L2, which are, for example, optical fiber and/or the
like.
The macro base station section 20 has a transmitting/receiving
antennas 201a and 201b, amplifying sections 202a and 202b,
transmitting/receiving sections 203a and 203b, a baseband signal
processing section 204, a scheduler 205, and a transmission path
interface 206. Transmission data that is transmitted from the macro
base station section 20 to a user terminal is input from an upper
station apparatus to the baseband signal processing section 204 via
the transmission path interface 206.
The baseband signal processing section 204 applies the following
processes to the downlink data channel signal. That is, for
example, a PDCP layer process, division and coupling of
transmission data, RLC (Radio Link Control) layer transmission
processes such as an RLC retransmission control transmission
process, MAC (Medium Access Control) retransmission control,
including, for example, an HARQ transmission process, scheduling,
transport format selection, channel coding, an inverse fast Fourier
transform (IFFT) process, and a precoding process, are performed.
Furthermore, as for the signal of the physical downlink control
channel, which is a downlink control channel, transmission
processes such as channel coding and inverse fast Fourier transform
are performed.
Also, the baseband signal processing section 204 notifies control
information for allowing each user terminal to communicate with the
macro base station section, to the user terminals connected with
the same cell, by a broadcast channel. Broadcast information for
allowing communication in the macro cell includes, for example, the
uplink or downlink system bandwidth, identification information of
a root sequence (root sequence index) for generating random access
preamble signals in the PRACH, and so on.
In the transmitting/receiving sections 203 and 203b, baseband
signals that are output from the baseband signal processing section
204 is subjected to frequency conversion into a radio frequency
band. The transmission signals having been subjected to frequency
conversion are amplified in the amplifying sections 202a and 202b
and output to the transmitting/receiving antennas 201a and
201b.
Meanwhile, as for signals to be transmitted on the uplink from the
user terminal to the macro base station section 20, radio frequency
signals that are received in the transmitting/receiving antennas
201a and 201b are amplified in the amplifying sections 202a and
202b, subjected to frequency conversion and converted into baseband
signals in the transmitting/receiving sections 203a and 203b, and
are input in the baseband signal processing section 204.
The baseband signal processing section 204 performs an FFT process,
an IDFT process, error correction decoding, a MAC retransmission
control receiving process, and RLC layer and PDCP layer receiving
processes, of the transmission data that is included in the
baseband signals received on the uplink. The decoded signals are
transferred to the upper station apparatus through the transmission
path interface 206. Note that a call processing section is included
as a functional element related to speech communication. The call
processing section performs call processes such as setting up and
releasing communication channels, manages the state of the macro
base station section 20 and manages the radio resources.
The micro base station B2 is formed with an RRH 30, which is placed
in a hot spot and/or the like, distant from the macro base station
B1, a cable L1, which is, for example, an optical cable, to connect
the RRH 30 to the macro base station B1, and a control/baseband
section 32, which is provided inside the macro base station B1. The
control/baseband section 32 basically constitutes the same
functional sections as the functional sections of the macro base
station section 20, not including the radio section, and has a
baseband signal processing section 33, and a scheduler 34 which
controls the resource allocation of the micro UE under the micro
cell and which also co-operates with the scheduler 205 of the macro
base station B1. Another micro base station B3 has the same
configuration as the micro base station B2.
FIG. 8 is a functional block diagram of a baseband signal
processing section 204 provided in the macro base station section
20. The baseband signal processing section 204 has a transmitting
section and a receiving section. The transmitting section of the
baseband signal processing section 204 has a channel signal
generating section 301, which generates a channel signal of a
downlink physical channel, and an OFDM modulation section 302,
which performs OFDM modulation of the channel signal of the
downlink physical channel generated in the channel signal
generating section 301.
The channel signal generating section 301 has a reference signal
generating section 311, a PDCCH generating section 312, a PHICH
generating section 313, and a PDSCH generating section 314. The
reference signal generating section 311 generates downlink
reference signals (CRS, UE-specific RS, DM-RS, CSI-RS and so on).
The reference signal generating section 311 is given MBSFN subframe
information from the scheduler 205, and does not generate CRSs to
be arranged in the data field in an MBSFN subframe. The PDCCH
generating section 312 generate a DCI (downlink scheduling
assignment, uplink scheduling grant), which is downlink control
information. The PHICH generating section 313 generates an ACK/NACK
in response to the user data received on the uplink. The PDSCH
generating section 314 generates a data channel signal, which is
downlink user data. Note that the PHICH generating section 313 is
given an ACK/NACK detection result with respect to user data
received on the uplink, from the ACK/NACK detection section 315.
Based on the content of the retransmission command input from the
upper station apparatus, the scheduler 205 schedules the uplink and
downlink control signals and uplink and downlink shared channel
signals with reference to these channel estimation value and
CQI.
The OFDM modulation section 302 generates a downlink transmission
signal by mapping downlink signals, which includes other downlink
channel signals and uplink resource allocation information signal,
to subcarriers, performs an inverse fast Fourier transform (IFFT),
and add CPs. FIG. 9 shows the function blocks of the OFDM
modulation section 302. The OFDM modulation section 302 is
configured to include a CRC adding section 101, a channel coding
section 102, an interleaver 103, a rate matching section 104, a
modulation section 105, and a subcarrier mapping section 106. The
CRC adding section 101 adds CRC bits for error check in packet data
units, to information bits that are input. Here, CRC bits that are
24-bit long are added to the information bits. Also, the CRC adding
section 101 adds CRC bits, per code block after code block
segmentation. The channel coding section 102 encodes packet data
including the CRC bits, using a predetermined coding scheme, at a
predetermined coding rate. To be more specific, the channel coding
section 102 performs Turbo coding at a coding rate of 1/3, and
acquires coded bits. The packet data is encoded into systematic
bits, and parity bits which are error control bits for these
systematic bits. The coding rate is designated from the scheduler
205. Although a case will be described here where Turbo coding of a
coding rate 1/3 is used, it is equally possible to use other coding
rates and other coding schemes as well. The interleaver 103
rearranges the order of the coded bits after channel coding
randomly (interleaving process). The interleaving process is
executed to minimize the data transmission loss due to burst
errors. The rate matching section 104 performs rate matching of the
coded bits by performing repetition and puncturing for the coded
bits. For example, the rate matching section 104 performs
puncturing when the coded bit length KW after channel coding is
greater than the coded bit length E after rate matching, and
performs repetition when the coded bit length KW after channel
coding is smaller than the coded bit length E after rate matching.
The modulation section 105 modulates the coded bits input from the
rate matching section 104 by a predetermined modulation scheme.
Note that the modulation scheme used in the modulation section 105
is given from the scheduler 205. The modulation scheme may be, for
example, QPSK (Quadrature Phase Shift Keying), 8PSK, 16QAM
(Quadrature Amplitude Modulation), and 64QAM. The coded bits
modulated by the modulation section 105 are transmitted to the
mobile terminal apparatus UE on the downlink as transmission
data.
The scheduler 205 determines the coding rate in the channel coding
section 102 and the modulation scheme in the modulation section 107
according to the current radio channel state. Also, the scheduler
205 performs retransmission control in accordance with response
signals (ACK/NACK) transmitted from user terminal. When a response
signal ACK (Acknowledge) is received, the corresponding
transmission packets in a buffer memory are removed. On the other
hand, when a response signal NACK (Non-Acknowledge) is received,
part or all of the corresponding transmission packets in the buffer
memory are extracted, and retransmitted to the user terminal via
the modulation section 105.
The receiving section of the baseband signal processing section 204
has a CP removing section 321, which removes the CPs from a
received signal, an FFT section 322, which performs a fast Fourier
transform (FFT) of the received signal, a subcarrier demapping
section 323, which demaps the signal after the FFT, a block
despreading section 324, which despreads the signal after
subcarrier demapping by a block spreading code (OCC), a cyclic
shift separating section 325, which separates the target user
signal by removing the cyclic shift from the signal after the
despreading, a channel estimation section 326, which performs
channel estimation with respect to the demapped signal after user
separation, a data demodulation section 327, which performs data
demodulation of the signal after subcarrier demapping using the
channel estimation value, and a data decoding section 328, which
performs data decoding of the signal after data demodulation.
The CP removing section 321 removes the parts corresponding to the
CPs and extracts the effective signal part. The FFT section 322
performs an FFT of the received signal and converts the signal into
a frequency domain signal. The FFT section 322 outputs the signal
after the FFT to the subcarrier demapping section 323. The
subcarrier demapping section 323 extracts the ACK/NACK signal,
which is an uplink control channel signal, from the frequency
domain signal, using resource mapping information. The subcarrier
demapping section 323 outputs the extracted ACK/NACK signal to the
data demodulation section 327. The subcarrier demapping section 327
outputs the extracted reference signals to the block despreading
section 324. The block despreading section 324 despreads the
received signals that have been orthogonal-multiplexed using an
orthogonal code (OCC) (block spreading code), using the orthogonal
code that is used in the user terminal. The block despreading
section 324 outputs the despread signal to the cyclic shift
separating section 325. The cyclic shift separating section 325
separates the control signals that have been orthogonal-multiplexed
using cyclic shifting, using cyclic shift numbers. Uplink control
channel signals from the user terminals are subjected to cyclic
shifting, in varying amounts of cyclic shift, on a per user basis.
Consequently, by applying a cyclic shift in the opposite direction
in the same amount of cyclic shift as the amount of cyclic shift
used in the user terminal, it is possible to separate the control
signals for the user targeted for the receiving process. The
channel estimation section 326 separates the reference signals,
orthogonal-multiplexed using cyclic shifting and orthogonal code,
using cyclic shift number and also using OCC numbers if necessary.
The channel estimation section 326 applies a cyclic shift in the
opposite direction using an amount of cyclic shift corresponding to
the cyclic shift number. Also, despreading is performed using the
orthogonal code corresponding to the OCC number. By this means, it
is possible to separate the user signal (reference signal). Also,
the channel estimation section 326 extracts the reference signals
received from the frequency domain signal using the resource
mapping information. Then, channel estimation is performed by
determining the correlation between the CAZAC code sequence
corresponding to the CAZAC number and the CAZAC code sequence that
is received. The data demodulation section 327 demodulates data
based on the channel estimation value from the channel estimation
section 326. Also, the data decoding section 328 performs data
decoding of the ACK/NACK signals after demodulation and outputs the
result as ACK/NACK information.
Based on this ACK/NACK information, the macro base station 20
determines transmitting a new PDSCH to the user terminal or
retransmitting the PDSCH that has been transmitted.
Next, the function blocks of the micro base station B2 will be
described. The RRH 30, which is one of the components to constitute
the micro base station B2, has antennas 201a and 201b, amplifying
sections 202a and 202b, transmitting/receiving sections 203a and
203b, which constitute the radio section of the macro base station
section 20.
The baseband signal processing section 33 of the micro base station
B2 has basically the same functional configuration as the baseband
signal processing section 204 of the macro base station section 20.
Although, in the following description, the function blocks of the
baseband signal processing section 33 of the micro base station B2
will be assigned the same codes as the codes assigned to the
function blocks of the baseband signal processing section 204 of
the macro base station section 20, "(B2)" will be assigned behind
the codes for distinction from the macro base station section 20.
That is to say, the transmitting section of the baseband signal
processing section 33 of the micro base station B2 has a channel
signal generating section 301 (B2), which generates a channel
signal of a downlink physical channel, and an OFDM modulation
section 302 (B2), which performs OFDM modulation of the channel
signal of the downlink physical channel generated in the channel
signal generating section 301 (B2).
The channel signal generating section 301 (B2) has a reference
signal generating section 311 (B2), a PDCCH generating section 312
(B2), a PHICH generating section 313 (B2), and a PDSCH generating
section 314 (B2). Also, upon receiving a command from the scheduler
34, the PDSCH generating section 314 (B2) sends information related
to the PDCCH starting position by higher layer signaling. Also, in
response to a command from the scheduler 34, the PDCCH generating
section 312 (B2) applies the X-PDCCH to a specific subframe. At
this time, as described above, to switch between several rate
matching methods dynamically, identification information of the
rate matching method to be applied is added to the downlink control
information. The PDCCH generating section 312 (B2) shifts the PDCCH
starting position according to a command from the scheduler 34
(FIG. 3). The operation of the OFDM modulation section 302 (B2) is
different from the OFDM modulation section 302 of the rate matching
section 104. As shown by dotted lines in FIG. 9, in the OFDM
modulation section 302 (B2), the scheduler 205 designates the rate
matching method (FIGS. 4A and 4B and FIGS. 5A and 5B) to the rate
matching section 104 (B2). The rate matching section 104 (B2)
switches the rate matching method dynamically in accordance with
commands from the scheduler 205. The designation of the rate
matching method is given from the scheduler 205 of the macro base
station B1, to the scheduler 34 of the micro base station B2. The
scheduler 205 and the scheduler 34 are elements that are embedded
in the same site of the macro base station B1 and are therefore
capable of dynamic cooperation.
Next, an overall configuration of a user terminal according to the
present embodiment will be described with reference to FIG. 10. A
user terminal 40 constituting a micro UE has a plurality of
transmitting/receiving antennas 401a and 401b, amplifying sections
402a and 402b, transmitting/receiving sections 403a and 403b, a
baseband signal processing section 404, and an application section
405.
Radio frequency signals received in the transmitting/receiving
antennas 401a, and 401b are amplified in the amplifying sections
402a and 402b, and, in the transmitting/receiving sections 403a and
403b, are subjected to frequency conversion and converted into a
baseband signal. This baseband signal is subjected to receiving
processes such as an FFT process, error correction decoding and
retransmission control, in the baseband signal processing section
404. In this downlink data, downlink user data is transferred to
the application section 405. The application section 405 performs
processes related to upper layers above the physical layer and the
MAC layer. Also, in the downlink data, broadcast information is
also transferred to the application section 405.
On the other hand, uplink user data is input from the application
section 405 to the baseband signal processing section 404. The
baseband signal processing section 404 performs a retransmission
control (HARQ) transmission process, channel coding, a DFT process,
and an IFFT process. The baseband signal output from the baseband
signal processing section 404 is converted into a radio frequency
band in the transmitting/receiving section 403. After that, the
amplifying sections 402a and 402b performs amplification and
transmits the result from the transmitting/receiving antennas 401a
and 401b.
FIG. 11 shows the function blocks of a user terminal in detail. In
the following description, a case will be described where, when
uplink control information is transmitted on the uplink from a user
terminal apparatus, a plurality of users are orthogonal-multiplexed
using cyclic shifting of a CAZAC code sequence, and retransmission
acknowledgement signals, which are feedback control information,
are transmitted. Note that, although, in the following description,
a case will be shown where retransmission acknowledgement signals
in response to a downlink shared channel received from two CCs are
transmitted, the number of CCs is not limited to this.
A user terminal 40 has a transmitting section and a receiving
section. The receiving section of the user terminal 40 has a
channel demultiplexing section 1400, which demultiplexes a received
signal into control information and the data signal, a data
information demodulation section 1401, which demodulates an OFDM
signal, a retransmission check section 1402, which checks
retransmission with respect to a downlink shared channel signal and
outputs a retransmission acknowledgement signal, a downlink control
information demodulation section 1403, which demodulates downlink
control information, and a de-rate matching method determining
section 1404, which determines the rate matching method related to
the received downlink shared channel signal and determines the
de-rate matching method. Meanwhile, the transmitting section of the
user terminal 40 has a control information transmission channel
selection section 1201, an uplink shared channel (PUSCH) processing
section 1000, an uplink control channel (PUCCH) processing section
1100, an SRS processing section 1300, a channel multiplexing
section 1202, an IFFT section 1203, and a CP attaching section
1204.
The data information demodulation section 1401 receives and
demodulates a downlink OFDM signal. That is to say, the data
information demodulation section 1401 removes the CPs from the
downlink OFDM signal, performs a fast Fourier transform, extracts
the subcarriers where a BCH signal or a downlink control signal is
allocated, and performs data demodulation. When downlink OFDM
signals are received from a plurality of CCs, data is demodulated
on a per CC basis. The data information demodulation section 1401
outputs the downlink signal after data demodulation, to the
retransmission check section 1402.
The retransmission check section 1402 determines whether or not a
downlink shared channel signal (PDSCH signal) that is received has
been received without error, and outputs an ACK if the downlink
shared channel signal has been received without an error or outputs
a NACK if an error is detected, and, if a downlink shared channel
signal is not detected, performs retransmission check with respect
to each state of the DTX, and outputs a retransmission
acknowledgement signal. When a plurality of CCs are allocated for
communication with the base station, whether or not the downlink
shared channel signal has been received without error is determined
on a per CC basis. Also, the retransmission check section 1402
detects the above three states on a per codeword basis. Upon
two-codeword transmission, the above three states are detected on a
per codeword basis. The retransmission check section 1402 outputs
the detection result to the transmitting section (here, the control
information transmission channel selection section 1201).
The downlink control information demodulation section 1403
demodulates the downlink control information from the radio base
station apparatus and detects the number of transport blocks and
the rate matching method. When a plurality of CCs are allocated for
communication with the base station, the number of blocks set for
each CC is detected. The downlink control information demodulation
section 1403 outputs the detection result of the number of
transport blocks to the channel selection control section 1101, and
outputs the rate matching method to the de-rate matching method
determining section 1404. The de-rate matching method determining
section 1404 determines the de-rate matching method corresponding
to the rate matching method of the PDSCH detected from the PDCCH,
as the PDSCH de-rate matching method.
The control information transmission channel selection section 1201
selects the channel to transmit the retransmission acknowledgement
signal, which is feedback control information. To be more specific,
whether the retransmission acknowledgement signal is included and
transmitted in the uplink shared channel (PUSCH) or transmitted by
the uplink control channel (PUCCH) is determined. For example, in a
subframe upon transmission, when there is a PUSCH signal, the
retransmission acknowledgement signal is output to the uplink
shared channel processing section 100, mapped to the PUSCH and
transmitted. On the other hand, when there is no PUSCH signal in
the subframe, the retransmission acknowledgement signal is output
to the uplink control channel (PUCCH) processing section 1100, and
is transmitted using the radio resource of the PUCCH.
The uplink shared channel processing section 1000 has a control
information bit determining section 1006, which determines the bits
of the retransmission acknowledgement signal based on the detection
result of the retransmission check section 1402, a channel coding
section 1007, which performs error correction coding of the
ACK/NACK bit sequence, a channel coding section 1001, which
performs error correction coding of the data sequence to be
transmitted, data modulation sections 1002 and 1008, which perform
data modulation of the data signal after coding, a time
multiplexing section 1003, which time-multiplexes the modulated
data signal and the retransmission acknowledgement signal, a DFT
section 1004, which performs a DFT (Discrete Fourier Transform) of
the time-multiplexed signal, and a subcarrier mapping section 1005,
which maps the signal after the DFT to subcarriers.
The uplink control channel (PUCCH) processing section 1100 has a
channel selection control section 1101, which controls the radio
resources of the PUCCH to use to transmit the retransmission
acknowledgement signal, a PSK data modulation section 1102, which
performs PSK data modulation, a cyclic shift section 1103, which
applies a cyclic shift to the data modulated in the PSK data
modulation section 1102, a block spreading section 1104, which
performs block spreading of the signal after cyclic shifting, by a
block spreading code, and a subcarrier mapping section 1105, which
maps the signal after block spreading to subcarriers.
The channel selection control section 1101 determines the radio
resource to use to transmit the retransmission acknowledgement
signal from the radio resources of the uplink control channel of a
PCC, with reference to a mapping table. The mapping table which the
channel selection control section 1101 uses defines the
combinations of retransmission acknowledgement signals in response
to the downlink shared channel signals of the PCC and the SCC using
a plurality of radio resources and bit information of phase
modulation. The channel selection control section 1101 changes the
content of the mapping table as appropriate according to the number
of transport blocks reported, acquired by demodulating the downlink
control information from the base station. To be more specific, it
is possible to apply content selecting predetermined parts of the
mapping table, depending on the number of transport blocks of the
PCC and SCC. The selection information is reported to the PSK data
modulation section 1102, the cyclic shift section 1103, the block
spreading section 1104 and the subcarrier mapping section 1105.
The PSK data modulation section 1102 performs phase modulation (PSK
data modulation) based on information reported from the channel
selection control section 1101. For example, in the PSK data
modulation section 1102, modulation into two bits of bit
information by QPSK data modulation is performed.
The cyclic shift section 1103 performs orthogonal multiplexing
using cyclic shifting of the CAZAC (Constant Amplitude Zero Auto
Correlation) code sequence. To be more specific, a time domain
signal is shifted through a predetermined amount of cyclic shift.
Note that the amount of cyclic shift varies per user, and is
associated with the cyclic shift indices. The cyclic shift section
1103 outputs the signal after the cyclic shift to the block
spreading section 1104. The block spreading section (orthogonal
code multiplication section) 1104 multiplies the reference signal
after cyclic shifting by an orthogonal code (performs block
spreading). Here, the OCC (block spreading code number) to use for
the reference signal may be reported by RRC signaling and so on
from an upper layer, or the OCC that is associated with the CS of
data symbol in advance may be used. The block spreading section
1104 outputs the signal after the block spreading to the subcarrier
mapping section 1105.
The subcarrier mapping section 1105 maps the signal after the block
spreading to subcarriers, based on information that is reported
from the channel selection control section 1101. Also, the
subcarrier mapping section 1105 outputs the mapped signal to the
channel multiplexing section 1202.
The SRS processing section 1300 has an SRS signal generating
section 1301, which generates an SRS signal (Sounding RS), and a
subcarrier mapping section 1302, which maps the SRS signal to
subcarriers. The subcarrier mapping section 1302 outputs the mapped
signal to the channel multiplexing section 1202.
The channel multiplexing section 1202 time-multiplexes the signal
from the uplink shared channel processing section 1000 or the
uplink control channel processing section, and the reference signal
from the SRS signal processing section 1300, and generates a
transmission signal including an uplink control channel signal.
The IFFT section 1203 performs an IFFT of the channel-multiplexed
signal and converts it into a time domain signal. The IFFT section
1203 outputs the signal after the IFFT to the CP attaching section
1204. The CP attaching section 1204 attaches CPs to the signal
after the orthogonal code multiplication. Then, an uplink
transmission signal is transmitted to the radio communication
apparatus using the uplink channel of the PCC.
Next, interference coordination according to the present embodiment
configured as described above will be described in detail.
The operations related to interference coordination, shown in FIG.
3 will be described. The macro base station B1 applies an ABS/MBSFN
frame in a specific subframe (for example, the second macro
cell-subframe shown in FIG. 3), arranges CRSs and PHICH only in the
first OFDM symbol of the macro cell subframe, and transmits a
downlink channel signal to a macro UE. In the macro base station
section 20, in the specific subframe, the reference signal
generating section 311 generates only the CRSs to multiplex on the
top OFDM symbol, and the PHICH generating section 313 generates an
ACK/NACK signal related to the UL grant eight subframes earlier.
Then, in the specific subframe, the PDCCH generating section 312
and the PDSCH generating section 314 do not generate channel
signals, thus creating a non-transmission period.
The micro base station B2 is reported information related to the
specific subframe from the macro base station B1. The information
about the specific subframe may be reported from the macro base
station B1 to the micro base station B2 by cooperation between the
scheduler 205 and the scheduler 34, or may be determined in advance
on a fixed basis.
The micro base station B2 transmits the PDCCH and the PDSCH in a
specific subframe that is reported. At this time, transmission
symbols are controlled such that the PDCCH starting position is
arranged shifted by one OFDM symbol, not to send the PDCCH in the
top one OFDM symbol of the micro cell subframe. The starting
position of the PDCCH is controlled in the PDCCH generating section
312 (B2) having received a command from the scheduler 205.
The micro base station B2 reports information related to the
specific subframe, where the PDCCH starting position is shifted, in
advance, so that the micro UE is able to demodulate the PDCCH
correctly. The information related to the specific subframe is
reported may be reported to the micro UE by higher layer
signaling.
When the user terminal 30, which serves as the micro UE, receives
the information related to the specific subframe by higher layer
signaling, the user terminal 30 saves the information of the
specific subframe. In the user terminal 30, the channel
demultiplexing section 1400 demultiplexes the downlink received
signal into downlink control information and data signal. The
downlink control information demodulation section 1403 normally
starts receiving the downlink control information from the top OFDM
symbol of a subframe and demodulates the PDCCH. Then, when
receiving the specific subframe reported in advance, the downlink
control information demodulation section 1403 starts receiving the
PDCCH from the second OFDM symbol of a subframe. The starting
position of the PDCCH in the specific subframe is by no means
limited to the second OFDM symbol, and, from the perspective of
reducing overhead, the specific subframe and the PDCCH starting
position are preferably linked.
By this means, even when the micro base station B2 shifts the
starting position of the PDCCH by one symbol and transmits the
PDCCH, the user terminal 30 is still able to recognize the starting
position of the PDCCH in the specific subframe and therefore
demodulate the PDCCH accurately. Consequently, even when the macro
base station B1 transmits CRSs and PHICH in the first OFDM symbol,
it is possible to demodulate the PDCCH accurately in the micro
cell.
Next, operations related to the interference coordination shown in
FIGS. 4A and 4B will be described. The macro base station B1
applies an ABS/MBSFN frame in a specific subframe (the second macro
cell subframe shown in FIGS. 4A and 4B), arranges CRSs only in the
first OFDM symbol of the macro cell subframe, and transmits the
downlink signal to the macro UE. In the macro base station section
20, in the specific subframe, the PDCCH generating section 312 and
the PDSCH generating section 314 do not generate channel signals,
thus providing a non-transmission period.
The micro base station B2 is reported information related to the
specific subframe from the macro base station B1. The information
about the specific subframe may be reported from the macro base
station B1 to the micro base station B2 (reporting by the
interference coordination method shown in FIG. 4A) by cooperation
between the scheduler 205 and the scheduler 34, or may be
determined in advance on a fixed basis.
The micro base station B2 transmits the X-PDCCH and the PDSCH in
the specific subframe reported, and transmits the DM-RS over the
entire system band. In the specific subframe, the X-PDCCH is
defined in the data field. Assuming that the top several OFDM
symbols (maximum three OFDM symbol) of the specific subframe are
the control field and the rest of the symbol field is the data
field, the X-PDCCH is transmitted by specific subcarriers in the
data field. The time-multiplexing and subcarrier mapping of the
X-PDCCH in the data field are performed in the OFDM modulation
section 302. The macro cell transmits the CRSs, PHICH and PCFICH
only in the control field, so that, in the micro cell, interference
against the X-PDCCH transmitted in the data field of the specific
subframe is prevented.
The micro base station B2 expands the channel signal (user data)
generated in the PDSCH generating section 314 (B2) to the control
field of the specific subframe. Micro cell CRSs are arranged in the
top OFDM symbol of the specific subframe, so that the PDSCH is
arranged in resources which do not overlap the micro cell CRSs in
the control field. However, when a cell ID that is different from
the macro cell is applied to the micro cell, there is interference
from the CRSs of the macro cell, and, as shown in FIG. 4A, in the
micro cell, the resource elements corresponding to the macro cell
CRSs are muted. In the micro cell subframe, resource elements that
are muted in the control field are subject to rate matching (the
first rate matching method). The PDCCH generating section 312 (B2)
generates downlink control information (DCI), to which the first
rate matching method is added.
Also, when the interference coordination shown in FIG. 4B is
selected, there is a possibility that the PHICH is transmitted in a
specific subframe of the macro cell. The PHICH is multiplexed on
resource elements that do not overlap the CRSs in the top OFDM.
Consequently, in the specific subframe of the micro cell, even in
resource elements that collide with the PHICH, the PDSCH suffers
interference. So, in the top OFDM symbol where the PHICH and CRSs
are arranged, starting transmitting the PDSCH from the second OFDM
symbol of the specific subframe, without arranging the PDSCH of the
micro cell, makes simpler design possible. In this case, in the
micro cell subframe, the first OFDM symbol of the control field is
entirely subject to rate matching (the second rate matching
method). The PDCCH generating section 312 (B2) generates downlink
control information (DCI), to which the second rate matching method
is added.
The scheduler 205 of the macro base station section 20 selects the
interference coordination method depending on whether or not the
PHICH is transmitted in the specific subframe and designates the
selected interference coordination method (which is linked to the
rate matching method) to the scheduler 34 of the micro base station
B2, and the scheduler 34 switches the rate matching method. The
rate matching section 104 (B2) of the OFDM modulation section 302
(B2) adopts the designated rate matching method. Also, the
scheduler 205 of the macro base station section 20 may select the
interference coordination method based on other elements than
whether or not the PHICH is transmitted in the specific
subframe.
The micro base station B2 reports information related to the
specific subframe where the X-PDCCH is applied, to the micro UE, in
advance, so that the micro UE is able to demodulate the PDCCH
correctly. The information related to the specific subframe may be
reported to the micro UE by higher layer signaling.
When the user terminal 30, which serves as the micro UE, receives
the information related to the specific subframe by higher layer
signaling, the user terminal 30 saves the information of the
specific subframe. In the user terminal 30, the channel
demultiplexing section 1400 demultiplexes the downlink received
signal into downlink control information and data signal. The
downlink control information demodulation section 1403 normally
starts receiving the downlink control information from the top OFDM
symbol of a subframe and demodulates the PDCCH. Then, when
receiving the specific subframe reported in advance, the downlink
control information demodulation section 1403 starts receiving the
X-PDCCH from the data field of a subframe. The rate matching method
added to the demodulated X-PDCCH is passed on to the rate matching
method determining section 1404. The de-rate matching method
determining section 1404 identifies the rate matching method of the
PDSCH transmitted in the specific subframe, and reports the de-rate
matching method of the PDSCH to the data information demodulation
section 1401. The data information demodulation section 1401
demodulates the PDSCH based on the de-rate matching method
reported. Consequently, even if the PDSCH rate matching method is
switched adaptively in the micro base station B2, it is still
possible to perform de-rate matching of the PDSCH adequately and
demodulate the PDSCH correctly.
Next, operations related to the interference coordination shown in
FIGS. 5A and 5B will be described. Although the macro cell and the
micro cell have the same cell ID, the same CRSs are allocated to
the same resource elements between the macro cell and the micro
cell. Although an ABS/MBSFN frame is adopted in a specific subframe
(the second macro cell subframe shown in FIGS. 5A and 5B), in FIG.
5B, the PDCCH is allocated to the control field of the macro cell
subframe. In other words, a protected subframe is also designed
such that the PDCCH can be transmitted in the macro cell.
When the micro base station B2 selects the interference
coordination of FIG. 5A, the selection of the interference
coordination of FIG. 5A is commanded from the scheduler 205 of the
macro base station section 20. In the micro base station B2, in the
specific subframe where the interference coordination of FIG. 5A is
selected, the X-PDCCH and the PDSCH are transmitted, and the DM-RS
is transmitted over the entire system band. Micro cell CRSs are
arranged in the top OFDM symbol of a specific subframe, so that the
PDSCH is arranged in resources that do not overlap the micro cell
CRS in the control field. The PDSCH can be arranged in resource
elements other than CRSs, so that rate matching is not necessary
(the case where rate matching is not necessary is referred to as
"the third rate matching method"). The PDCCH generating section 312
(B2) generates downlink control information (DCI) to which the
third rate matching method is added.
When the interference coordination of FIG. 5B is selected, the
selection of the interference coordination of FIG. 5B is commanded
from the scheduler 205 of the macro base station section 20 to the
micro base station B2. The micro base station B2 transmits the
X-PDCCH and the PDSCH in the specific subframe where the
interference coordination of FIG. 5B is selected, and transmits the
DM-RS over the entire system band. Since the CRSs and PDCCH of the
micro cell are arranged in the top OFDM symbol of the specific
subframe, the PDSCH is arranged in the top resource of the data
field, without arranging the PDSCH in the control field.
Consequently, the rate matching section 104 (B2) performs rate
matching with respect to the entire control field, in accordance
with the command from the scheduler 34 (the fourth rate matching
method). The PDCCH generating section 312 (B2) generates downlink
control information (DCI), to which the fourth rate matching
method.
The scheduler 205 of the macro base station section 20 determines
the rate matching method depending on whether or not the PDCCH is
transmitted in a protected subframe, and designates the determined
rate matching method to the scheduler 34 of the micro base station
B2, and the scheduler 34 switches the rate matching method on a
dynamic basis. The operations in the user terminal 30, which serves
as the micro UE, are the same as described above.
Although, in the above description, the RRH 30 has been described
as an example of a small transmission power node, a pico base
station, a femto base station and so on are equally applicable.
FIG. 12 shows a system configuration diagram in which a pico base
station (or a femto base station), instead of an RRH, cooperates
with the macro base station B1. As shown in this drawing, the macro
base station B1 and the pico base station (or the femto base
station) are formed basically with the same function blocks. That
is to say, the pico base station (the femto base station) has
transmitting/receiving antennas 2201a and 2201b, amplifying
sections 2202a and 2202b, transmitting/receiving sections 2203a and
2203b, a baseband signal processing section 2204, a scheduler 2205,
and a transmission path interface 2206. The macro base station B1
and the pico base station are connected so as to be able to
communicate with each other, via, for example, an X2 interface.
Also, although, in the above description, a non-transmission
period, in which the macro base station stops transmitting signals
while leaving minimal quality measurement signals, has been
described as an example of a specific subframe, subframes outside a
non-transmission period are equally applicable.
Now, although the present invention has been described in detail
with reference to the above embodiments, it should be obvious to a
person skilled in the art that the present invention is by no means
limited to the embodiments described in this specification. For
example, the number of users and the number of processing sections
in the devices in the above embodiment are by no means limiting,
and it is equally possible to change these as appropriate depending
on devices. The present invention can be implemented with various
corrections and in various modifications, without departing from
the spirit and scope of the present invention defined by the
recitations of the claims. Consequently, the descriptions in this
specification are provided only for the purpose of explaining
examples, and should by no means be construed to limit the present
invention in any way.
The disclosure of Japanese Patent Application No. 2011-029081,
filed on Feb. 14, 2011, including the specification, drawings and
abstract, is incorporated herein by reference in its entirety.
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